1. Field of the Invention
The present invention relates to a pyrometer adapter for mounting a pyrometer in a gas turbine engine, and, more specifically, to a pyrometer adapter which accommodates relative motion between two mounting surfaces in the gas turbine engine.
2. Description of Related Art
Pyrometers are well-known for the measurement of temperature at certain hot areas in a gas turbine engine, such as turbine blades. Generally, such measurement is performed by exposing the pyrometer to infrared light in the targeted area, from which the temperature is determined by the bandwidth thereof. Typical of such pyrometers is that shown in U.S. Pat. No. 4,687,344 to Lillquist.
Because the pyrometer must be able to sense the light representing the thermal energy at the targeted area, an adapter is provided to penetrate applicable casings, liners, or the like. For example, in order to determine the temperature of a turbine blade, the pyrometer must be able to penetrate the turbine casing and the outer band of the turbine nozzle. This has been done in the past by means of a pyrometer adapter which includes a sight tube retained within a socket on the nozzle outer band (such as on a boss thereof). The prior art pyrometer adapter further includes a second tube concentric with and radially outside the sight tube, with a flanged end adapted for mounting to the turbine casing.
It is well-known that the nozzle outer band and the turbine casing are made of materials having different coefficients of expansion and are physically located in different proximity with respect to the thermal energy in the turbine. Accordingly, the nozzle outer band and the turbine casing thermally grow at differing rates, which causes relative motion between the outer tube and the sight tube of the pyrometer adapter. In order to sustain or accommodate this relative motion, a spherical bearing has been utilized at the junction of the sight tube and the outer tube, which allows the sight tube and outer tube to pivot. However, as the ambient temperature of gas turbine engines has increased (approximately 1200.degree. F.), it has been found that such a spherical bearing seizes and therefore does not reliably accommodate the relative motion. Moreover, the spherical bearing is not able to readily adjust to relative motion in three planes.